It seems like you just make the seventh note flat, but are there any restrictions to that? Can any scale become a Dominant Seventh Scale by slight modification? Or does it differ on a case-by-case basis?

3 Answers
3

The Dominant 7th scale is one of the many named scales used in a jazz context.

It should be like the major scale, but with a flat 7th. From Jamey Aebersold's Scale Syllabus, it has the following pattern of whole and half steps: W W H W W H W (in C: C D E F G A Bb C). This is also commonly known as the mixolydian scale.

Many scales do have a flat 7th, but if it is not based on the major scale with the above pattern, it would have a different name.

Lastly, it is accepted to refer to a flat 7th itself, that is, the scale degree or note, as a dominant 7th.

So, all of the major scales can become a mixolydian scale, is that right?
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DanteJun 3 '12 at 2:19

If by 'all of the major scales' you mean 'the major scale starting on any root note,' then yes. Any relative-pitch transformation that is true for one type of scale is true for that scale in any key, but keep in mind that "Flatting the 7th" simply means to lower by a semitone. For F# major, for example, the 7th is normally named E#. To "flat" that 7th note to make a dominant 7th, it is going to end up as E natural.
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NReilingh♦Jun 3 '12 at 3:46

When considering scales rather than chords as in the ABRSM syllabus where dominant 7th scales are required, the dominant 7th scale consists of the major triad with minor 7th note but starting on the dominant note of the scale i.e. the dominant 7th of C is G,B,D,F or in other words, the arpeggio on the mixolydian scale of C. I found this out today while researching for grade 8.